1. Field of the Invention
The invention relates to a belt driven spindle and sheave mechanism as used in multi-spindle mowers.
2. Description of the Related Art:
The invention relates to blade drive mechanisms for mowers and, more specifically, to belt driven spindle and sheave arrangements for multi-spindle mower decks. Conventional mowers provide an engine or motor which drives a belt. This belt engages and drives a pulley or sheave mounted on the upper portion of a shaft or spindle. The spindle is rotatably supported by bearings within a housing carried by the mower deck or frame. The lower portion of the spindle extends below the housing and has a mower blade mounted thereto for rotation with the spindle.
In conventional belt driven mowers, a cylindrical hub is welded to the sheave at its center. The hub is then placed over the spindle. A keyway is formed in the hub and spindle such that when a key is placed in the keyway, the spindle is thereby fixed for rotation with the hub and sheave. Threads are formed on the spindle above the hub such that a nut can be placed on the spindle in contact with the hub to keep the hub from coming off the upper end of the spindle.
A second embodiment of the prior art comprises a belt engaging sheave having a toothed or splined opening at its center. A first bushing with teeth or splines that correspond to those in the opening of the sheave is positioned on the spindle. A keyway is formed in the first bushing and the spindle such that when a key is placed in the keyway, the spindle and first bushing will rotate together. The sheave is placed on the first bushing such that as the sheave is rotated by the belt, the teeth in the sheave confront the teeth in the first bushing and rotate the first bushing and spindle. Threads are formed in the spindle above the sheave such that when a washer and nut are placed on the threads, the sheave and first bushing remain on the spindle.
A third embodiment of the prior art, as described in U.S. Pat. No. 3,916,706 comprises a sheave engaging hub that has a flattened portion in its center opening. The flattened portion engages a corresponding flattened portion of the spindle during operation, which keeps the spindle fixed for rotation with the hub and sheave.
In these conventional mowers, the hub or toothed bushing rides in contact with a second bushing. The second bushing is mounted on the spindle and rides on the inner race of a first bearing. The bearing supports the spindle for rotation about its axis. A spacer is placed on the spindle between the first bearing and a second bearing. Several mechanisms are mounted on the spindle beneath the second bearing that serve to carry the mower blade, shield the contents of the housing from debris, and create a seal for the bearings.
Such conventional spindle and sheave constructions serve to fix the spindle to the sheave for rotation therewith. For the motor and drive belt to rotate the blade, the spindle must be fixed to the sheave and not slip thereon. Also, during mower operations the blade may encounter large objects such as stones or thick vegetation that can retard or prevent rotation of the blade and therefore prevent the spindle from rotating. If the spindle rotation is stopped, but the drive belt continues to power the sheave carried on the spindle, the structure used to secure the sheave to the spindle for rotation therewith may fail. To prevent such failures keys, keyways and/or welds have been used between the sheave and spindle. If the spindle is not tightly secured to the sheave and rotates relative to the sheave when the blade encounters thick vegetation, the vegetation may be improperly cut. The relative motion between the spindle and sheave due to impact loading from large objects such as stones or stumps can cause wearing of contact surfaces within the mechanism and may result in the early failure of the mechanism.
It is therefore desirable to provide a mechanism which meets the need for fixing the spindle to the sheave during initiation of operation and during operation as impact loads are imparted to the mower blade.
A main disadvantage of these conventional sheave and spindle mechanisms is their cost of manufacture and assembly. In the conventional welded hub mechanism, the hub and key must be manufactured. The hub must be welded to the sheave which is time consuming and expensive. The keyway must be formed in the hub and spindle, and the key placed therein, all of which are costly processes. Similarly, in the second conventional mechanism, involving the toothed bushing, the toothed bushing and key are separately manufactured. The keyway must be formed in the toothed bushing and the spindle and the key placed therein. Therefore, it would be desirable to provide a reliable spindle and sheave construction that alleviates keys, keyways and/or welding to secure the sheave to the spindle and one which also involves few parts and is inexpensive to manufacture and assemble.
Because of the number of parts used in conventional mechanisms to fix the spindle to the sheave for rotation therewith, there is potential for inaccuracies in their operation. The hub of the conventional mechanism is welded to the sheave. This is a potentially inaccurate process that may cause the hub to be mounted in a non-perpendicular manner with respect to the plane of the sheave. Also, an inaccurate weld may cause the hub to be mounted off-center within the sheave. Even if welded perfectly, the hub may introduce additional inaccuracies due to the tolerances between hub outer diameter plus the hub inner diameter and clearance between the hub and its mating parts. The conventional mechanisms utilizing toothed bushings similarly involve the potential for inaccuracies. The cumulative effect of the manufacturing tolerances of the toothed opening in the sheave, the teeth of the bushing, the hole in the center of the bushing and the spindle can result in the spindle and sheave being eccentrically mounted. The cumulative effect of the tolerances may also result in the spindle being fixed in a non-perpendicular manner with respect to the sheave. Such eccentric and non-perpendicular mounting of the spindle may result in a whipping effect in the belt which contributes to belt wear. Idler pulleys and tensioner pulley mechanisms compensate for and accommodate belt whip, causing noise and vibration of the vehicle. Therefore, it is desirable to provide a mechanism for accurately assembling and mounting the spindle within the sheave such that belt deterioration, vibration and noise caused by belt whip are reduced.
The spindle of the conventional mechanism is vertically fixed within the bearings. To accomplish this fixed position, the spindle is force fitted through the inner race of the bearing which imparts an impact load on the ball bearings and the surfaces with which the ball bearings have contact. The impact of the ball bearings against the inner and outer races of the bearing can cause dents or dimples to form in the races where the impact occurs. These dents within the bearing races can contribute to the deterioration and early failure of the bearing. Therefore, it is desirable to provide a spindle and sheave arrangement that does not require the spindle to be force fitted through the bearings.